Such steering arrangements are, for example, available from Sauer-Danfoss (Nordborg) A/S, Nordborg, Denmark.
Such steering arrangements are mainly used in tractors and other mobile equipment. In a housing, the steering arrangement has an outer rotary slide and an inner rotary slide, which are connected with each other via a spring. When the inner rotary slide and the outer rotary slide are turned relative to each other, various throttles are opened or closed. For example, the throttling device in the supply path and the return throttle in the return path are opened, whereas the bypass throttle is closed. However, the bypass throttle and the throttles of the throttling device or the return throttle, respectively, have an overlap area, in which all throttles are open at the same time. The opening width of the throttles is determined by the relative angular position between the inner and the outer rotary slide. Hydraulic fluid flows through the throttling device and the measuring motor in the supply path. In this connection, the measuring motor resets the outer rotary slide in relation to the inner rotary slide, that is, returns them to their neutral positions, so that, in dependence of the deflection of a steering handwheel, a defined amount of hydraulic fluid can be permitted to flow to the steering motor. Thus, it is ensured that the position of the steered member has a certain relation to the angular position of the steering handwheel.
Such a steering arrangement has proved its value in connection with land vehicles. However, problems occur, when such a steering arrangement is to be used in a motorboat. This particularly applies, when the motorboat is configured for high speeds, that is, speeds of 100 km/h and higher. In a motorboat, the steering motor acts upon a rudder or the complete driving motor that includes the driving propeller. When the boat is at high speed, relatively large forces are counteracting upon the steering motor and thus upon the steering arrangement via the rudder or the driving motor, particularly in connection driving along a curve. These high pressures can also occur when driving straight because at high speeds the driving propeller is no longer completely immersed in the water. In this case, the propeller generates large side pressures. When, in connection with a land vehicle, a load of the steering motor in the magnitude of 5 to 10 bar can be assumed, the pressure when using the steering arrangement in a motorboat can range from 35 to 50 bar.
Usually, these large pressures can be managed particularly when the pressure is positive. Problems occur, where negative loads are concerned. In this case, situations may occur, in which the rudder is moved faster than specified by the steering handwheel or another steering device.
Based on the foregoing, it is the general object of the present invention to provide a hydraulic steering arrangement suitable for fast motorboats that improves upon or overcomes the problem and drawbacks associated with the prior art.